computed
computed : 创建计算属性
<html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta http-equiv="X-UA-Compatible" content="ie=edge"> <title>Hello Vue3.0</title> <style> body, #app { text-align: center; padding: 30px; } </style> <script src="../../packages/vue/dist/vue.global.js"></script> </head> <body> <h3>computed</h3> <div id='app'></div> </body> <script> const { createApp, reactive, ref, computed } = Vue const App = { template: ` <button @click='handleClick'>count++</button> <div style="margin-top: 20px">{{ count }}</div> `, setup() { const refData = ref(0); const count = computed(()=>{ return refData.value; }) const handleClick = () =>{ refData.value += 1 // 要修改 count 的依赖项 refData } console.log("refData:" , refData) return { count, handleClick } } } createApp(App).mount('#app') </script> </html>
<html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta http-equiv="X-UA-Compatible" content="ie=edge"> <title>Hello Vue3.0</title> <style> body, #app { text-align: center; padding: 30px; } </style> <script src="../../packages/vue/dist/vue.global.js"></script> </head> <body> <h3>computed</h3> <div id='app'></div> </body> <script> const { createApp, reactive, ref, computed } = Vue const App = { template: ` <button @click='handleClick'>count++</button> <div style="margin-top: 20px">{{ count }}</div> `, setup() { const refData = ref(0); const count = computed({ get(){ return refData.value; }, set(value){ console.log("value:", value) refData.value = value; } }) const handleClick = () =>{ count.value += 1 // 直接修改 count } console.log(refData) return { count, handleClick } } } createApp(App).mount('#app') </script> </html>
watch & watchEffect
watch : 创建 watch 监听watchEffect : 如果响应性的属性有变更，就会触发这个函数
<html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta http-equiv="X-UA-Compatible" content="ie=edge"> <title>Hello Vue3.0</title> <style> body, #app { text-align: center; padding: 30px; } </style> <script src="../../packages/vue/dist/vue.global.js"></script> </head> <body> <h3>watch && watchEffect</h3> <div id='app'></div> </body> <script> const { createApp, reactive, ref, watch, watchEffect } = Vue const App = { template: ` <div class="container"> <button style="margin-left: 10px" @click="handleClick()">按钮</button> <button style="margin-left: 10px" @click="handleStop">停止 watch</button> <button style="margin-left: 10px" @click="handleStopWatchEffect">停止 watchEffect</button> <div style="margin-top: 20px">{{ refData }}</div> </div>` , setup() { let refData = ref(0); const handleClick = () =>{ refData.value += 1 } const stop = watch(refData, (val, oldVal) => { console.log('watch ', refData.value) }) const stopWatchEffect = watchEffect(() => { console.log('watchEffect ', refData.value) }) const handleStop = () =>{ stop() } const handleStopWatchEffect = () =>{ stopWatchEffect() } return { refData, handleClick, handleStop, handleStopWatchEffect } } } createApp(App).mount('#app') </script> </html>
v-model
v-model：就是双向绑定
<html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta http-equiv="X-UA-Compatible" content="ie=edge"> <title>Hello Vue3.0</title> <style> body, #app { text-align: center; padding: 30px; } </style> <script src="../../packages/vue/dist/vue.global.js"></script> </head> <body> <h3>v-model</h3> <div id='app'></div> </body> <script> const { createApp, reactive, watchEffect } = Vue const App = { template: `<button @click='click'>reverse</button> <div></div> <input v-model="state.message" style="margin-top: 20px" /> <div style="margin-top: 20px">{{ state.message }}</div>`, setup() { const state = reactive({ message:'Hello Vue 3!!' }) watchEffect(() => { console.log('state change ', state.message) }) click = () => { state.message = state.message.split('').reverse().join('') } return { state, click } } } createApp(App).mount('#app') </script> </html>
readonly
使用 readonly 函数，可以把 普通 object 对象、reactive 对象、ref 对象 返回一个只读对象。
返回的 readonly 对象，一旦修改就会在 console 有 warning 警告。
程序还是会照常运行，不会报错。
<html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta http-equiv="X-UA-Compatible" content="ie=edge"> <title>Hello Vue3.0</title> <style> body, #app { text-align: center; padding: 30px; } </style> <script src="../../packages/vue/dist/vue.global.js"></script> </head> <body> <h3>readonly</h3> <div id='app'></div> </body> <script> const { createApp, reactive, readonly, watchEffect } = Vue const App = { template: ` <button @click='click'>reverse</button> <button @click='clickReadonly' style="margin-left: 20px">readonly++</button> <div style="margin-top: 20px">{{ original.count }}</div> `, setup() { const original = reactive({ count: 0 }) const copy = readonly(original) watchEffect(() => { // works for reactivity tracking console.log(copy.count) }) click = () => { // mutating original will trigger watchers relying on the copy original.count++ } clickReadonly = () => { // mutating the copy will fail and result in a warning copy.count++ // warning! } return { original, click, clickReadonly } } } createApp(App).mount('#app') </script> </html>
provide & inject
provide 和 inject 启用类似于 2.x provide / inject 选项的依赖项注入。
两者都只能在 setup() 当前活动实例期间调用。
import { provide, inject } from 'vue' const ThemeSymbol = Symbol() const Ancestor = { setup() { provide(ThemeSymbol, 'dark') } } const Descendent = { setup() { const theme = inject(ThemeSymbol, 'light' /* optional default value */) return { theme } } }
inject 接受可选的默认值作为第二个参数。
如果未提供默认值，并且在 Provide 上下文中找不到该属性，则 inject 返回 undefined。
Lifecycle Hooks
Vue2 与 Vue3 的生命周期勾子对比：
| Vue2 | Vue3 |
| :------ | :------ |
| beforeCreate | setup(替代) |
| created | setup(替代) |
| beforeMount | onBeforeMount |
| mounted | onMounted |
| beforeUpdate | onBeforeUpdate |
| updated | onUpdated |
| beforeDestroy | onBeforeUnmount |
| destroyed | onUnmounted |
| errorCaptured | onErrorCaptured |
| 空 | onRenderTracked |
| 空 | onRenderTriggered |
除了 2.x 生命周期等效项之外，Composition API 还提供了以下调试挂钩：
onRenderTrackedonRenderTriggered
这两个钩子都收到一个 DebuggerEvent，类似于观察者的 onTrack 和 onTrigger 选项：
export default { onRenderTriggered(e) { debugger // inspect which dependency is causing the component to re-render } }
例子：
<html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta http-equiv="X-UA-Compatible" content="ie=edge"> <title>Hello Vue3.0</title> <style> body, #app { text-align: center; padding: 30px; } </style> <script src="../../packages/vue/dist/vue.global.js"></script> </head> <body> <h3>Lifecycle Hooks</h3> <div id='app'></div> </body> <script> const { createApp, reactive, onMounted, onUpdated, onUnmounted } = Vue const App = { template: ` <div class="container"> <button @click='click'>reverse</button> <div style="margin-top: 20px">{{ state.message }}</div> </div>` , setup() { console.log('setup!') const state = reactive({ message: 'Hello Vue3!!' }) click = () => { state.message = state.message.split('').reverse().join('') } onMounted(() => { console.log('mounted!') }) onUpdated(() => { console.log('updated!') }) onUnmounted(() => { console.log('unmounted!') }) return { state, click } } } createApp(App).mount('#app') </script> </html>
